This invention relates generally to electromagnetic flowmeters, and more particularly to a flangeless flowmeter whose components are integrated to form a highly compact, low-cost unit that may be readily installed in a flow line.
Magnetic flowmeters such as those disclosed in U.S. Pat. Nos. 3,695,104; 3,824,856; 3,783,687 and 3,965,738, are especially adapted to measure the volumetric flow rates of fluids which present difficult handling problems, such as corrosive acids, sewage and slurries. Because the instrument is free of flow obstructions, it does not tend to plug or foul. The flowmeter can be used to meter liquids without regard to heterogenous consistency.
An added advantage of an obstructionless construction is that pressure losses are reduced to levels encountered in equivalent lengths of equal diameter pipeline, thereby reducing or conserving pressure source requirements in new or existing hydraulic lines as compared to other metering techniques.
In a magnetic flowmeter, an electromagnetic field is generated whose lines of flux are mutually perpendicular to the longitudinal axis of the flow tube through which the fluid to be metered is conducted and to the transverse axis along which the electrodes are located at diametrically-opposed positions with respect to the tube. The operating principles are based on Faraday's law of induction, which states that the voltage induced across any conductor as it moves at right angles through a magnetic field will be proportional to the velocity of that conductor. The metered fluid effectively constitutes a series of fluid conductors moving through the magnetic field; the more rapid the rate of flow, the greater the instantaneous value of the voltage established at the electrodes.
Typical of commercially-available electromagnetic flowmeters is that unit manufactured by Fischer & Porter Co. of Warminster, Pa., whose Model 10D1430 flowmeter is described in Instruction Bulletin 10D1430A-1-Revision 4. This meter consists of a carbon-steel pipe spool flanged at both ends and serving as a meter body. Saddle-shaped magnetic coils are fitted on opposite sides of the inner surface of the meter body, the magnetically-permeable pipe spool acting as a core or return path for the magnetic field generated by these coils.
The coils in this known form of meter are potted within an epoxy-based compound. An interior liner of neoprene or similar insulating material is inserted within the pipe and turned out against the faces of the mounting flanges. Disposed at diametrically-opposed positions within the central portion of the meter body are two cylindrical electrodes that are insulated from the pipe, the faces of the electrodes being flush with the inner surface of the pipe and coming in contact with the fluid to be metered. Connected to these electrodes and housed in a box external to the pipe are calibration components and a pre-amplifier.
In installing a standard magnetic flowmeter of the above-described type, the meter is interposed between the upstream and downstream pipes of a fluid line, each pipe having an end flange. The mounting flanges on the meter are bolted to the flanges of line pipes. It is, of course, essential that the circle of bolt holes on the mounting flanges of the meter match those on the pipe flanges.
In a magnetic flowmeter, the flow tube is subjected to the same fluid pressure as the line pipes. The flow tube must therefore be of a material and of a thickness sufficient to withstand this pressure, even though the strength of the flow tube is unrelated to its measuring function. This design factor contributes significantly to the cost of a standard meter. Existing meters of the above-described type which are made up of components that must be assembled are generally of substantial size and weight and quite expensive to manufacture.